Goal
The objective of this research is to measure physical, chemical, mechanical, and hydrologic property changes in methane hydrate-bearing sediments subjected to injection of carbon dioxide and nitrogen.

Background
A number of studies have investigated the impact of injecting carbon dioxide (CO2) and CO2-nitrogen (N2) mixtures into methane hydrate for the purpose of sequestering CO2 and releasing methane (CH4), and review articles have been published summarizing the literature. Most of these studies have investigated the fundamental physical/chemical nature of the exchange of CO2 and/or N2 with CH4 in the clathrate. These studies have helped identify the limits of the effectiveness of CO2 injection into methane hydrate for the purposes of methane production and CO2 sequestration.

Few studies have examined the hydrologic and physical/mechanical property changes that occur during a hydrate composition change. In the few studies that have been conducted, researchers did not measure hydrologic properties; quantification of the effluent gas was crude and performed over a limited range of conditions (mostly dry hydrate) and failed to address important reservoir issues such as pressure increase upon injection and the effect of changes in gas composition in a system where the gas composition varies.

This research will investigate processes associated with the injection of N2, CO2, and mixtures of these gases into methane hydrate-bearing porous media under non-stirred batch and flow-through conditions, and will attempt to quantify the exchange kinetics of the N2 and CO2 replacement into methane hydrate using flow-through reactors and breakthrough curve analysis. Permeability will be measured to detect changes, and geophysical property changes will be measured using either the Split Hopkinson Resonant Bar apparatus or a flow-through vessel with p- and s- wave transducers in the end platens.

Impact
The primary benefits of this lab-based research are improved empirical relationships among physical, chemical, mechanical, and hydrologic property changes in methane hydrate-bearing sediments subjected to injection of CO2and N2, which will assist in understanding the results of hydrate production field test data.

Accomplishments (most recent listed first)

Budget Period 3 (June 2013 – May 2014)

Rebuilt hydrate pressure vessel.

Redesigned and built new temperature control jacket allowing teflon coating of pressure vessel to eliminate external corrosion.

Completed development of computational protocol to provide theoretical distribution of hydrates in an experimentally measured sediment matrix.

Developed the permeability and diffusivity calculation codes for use in grain-scale computation of hydrate-bearing sediment properties based on micro CT sample descriptions.

Completed initial experiments measuring kinetics of gas exchange between a CO2 / N2 mixture and existing CH4 hydrate in a system with excess free water and comparing it to a system without excess free water.

Budget Period 1 (June 2012 – May 2013)

Completed and documented results of a series of lab tests to monitor changes (gas exchange rates, permeability, and geomechanical properties) in CH4 hydrate-bearing samples exposed to an N2/CO2 gas mixture.

Completed design and construction of an experimental system to measure kinetics of gas exchange in hydrate-bearing sediments.

Established a new laboratory set-up (including new CT scanner) capable of performing and monitoring hydrate exchange kinetics experiments.

Please see the project page for ESD05-048 to view accomplishments from past, related efforts.

Current Status (January 2015)
Budget period 3 activities are ongoing. Over the coming months, hydrate pressure vessel endcaps will be modified allowing placement of heat flux sensors in the test region adjacent to the sample. Samples will be prepared using either natural anisotropic sandstone or layered packed sand. The experimental apparatus will then be assembled within which heat flux and temperature will be monitored during hydrate formation and dissociation. Researchers will attempt to monitor heat flux both parallel and perpendicular to the applied bedding.